CELERY

1. Installation - pip install django-celery

2. Add

3. Basic project structure.

    - src/
      - bin/celery_worker_start # will be explained later on
      - logs/celery_worker.log
      - stack/__init __.py
      - stack/celery.py
      - stack/settings.py
      - stack/urls.py
      - manage.py
   

4. Add celery.py file to your stack/stack/ folder.

    from __future__ import absolute_import
    import os
    from celery import Celery
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'stack.settings')
    from django.conf import settings  # noqa
    app = Celery('stack')
    app.config_from_object('django.conf:settings')
    app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)
   

5. to your stack/stack/__init__.py add following code:

    from __future__ import absolute_import
    from .celery import app as celery_app  # noqa
   

6. Create a task and mark it for example as @shared_task()

    @shared_task()
    def add(x, y):
        print("x*y={}".format(x*y))
   

7. Running celery worker "by hand":

   celery -A stack worker -l info if you also want to add

1. Create a script to start celery worker. Insert your script within your app. For example: stack/bin/celery_worker_start

    #!/bin/bash
    
    NAME="StackOverflow Project - celery_worker_start"
    
    PROJECT_DIR=/home/stackoverflow/apps/proj/proj/
    ENV_DIR=/home/stackoverflow/apps/proj/env/
    
    echo "Starting $NAME as `whoami`"
    
    # Activate the virtual environment
    cd "${PROJECT_DIR}"
    
    if [ -d "${ENV_DIR}" ]
    then
        . "${ENV_DIR}bin/activate"
    fi
    
    celery -A stack --loglevel='INFO'
   

2. Add execution rights to your newly created script:

   chmod u+x bin/celery_worker_start

3. Install supervisor (skip this test if supervisor already installed)

   apt-get install supervisor

4. Add config file for your supervisor in order to start you celery. Place it in /etc/supervisor/conf.d/stack_supervisor.conf

    [program:stack-celery-worker]
    command = /home/stackoverflow/apps/stack/src/bin/celery_worker_start
    user = polsha
    stdout_logfile = /home/stackoverflow/apps/stack/src/logs/celery_worker.log
    redirect_stderr = true
    environment = LANG = en_US.UTF-8,LC_ALL = en_US.UTF-8
    numprocs = 1
    autostart = true
    autorestart = true
    startsecs = 10
    stopwaitsecs = 600
    priority = 998
   

5. Reread and update supervisor

    sudo supervisorctl reread
        stack-celery-worker: available
    sudo supervisorctl update
        stack-celery-worker: added process group
   

6. Basic commands

    sudo supervisorctl status stack-celery-worker                       
        stack-celery-worker      RUNNING    pid 18020, uptime 0:00:50
    sudo supervisorctl stop stack-celery-worker  
        stack-celery-worker: stopped
    sudo supervisorctl start stack-celery-worker                        
        stack-celery-worker: started
    sudo supervisorctl restart stack-celery-worker 
        stack-celery-worker: stopped
        stack-celery-worker: started
   

Celery requires a broker to handle message-passing. We use RabbitMQ because it’s easy to setup and it is well supported.

Install rabbitmq using the following command

sudo apt-get install rabbitmq-server

Once the installation is complete, create user, add a virtual host and set permissions.

sudo rabbitmqctl add_user myuser mypassword
sudo rabbitmqctl add_vhost myvhost
sudo rabbitmqctl set_user_tags myuser mytag
sudo rabbitmqctl set_permissions -p myvhost myuser ".*" ".*" ".*"

To start the server:

sudo rabbitmq-server

We can install celery with pip:

pip install celery

In your Django settings.py file, your broker URL would then look something like

BROKER_URL = 'amqp://myuser:mypassword@localhost:5672/myvhost'

Now start the celery worker

celery -A your_app worker -l info

This command start a Celery worker to run any tasks defined in your django app.

Supervisor is a Python program that allows you to control and keep running any unix processes. It can also restart crashed processes. We use it to make sure Celery workers are always running.

First, Install supervisor

sudo apt-get install supervisor

Create your_proj.conf file in your supervisor conf.d (/etc/supervisor/conf.d/your_proj.conf):

[program:your_proj_celery]
command=/home/your_user/your_proj/.venv/bin/celery --app=your_proj.celery:app worker -l info
directory=/home/your_user/your_proj
numprocs=1
stdout_logfile=/home/your_user/your_proj/logs/celery-worker.log
stderr_logfile=/home/your_user/your_proj/logs/low-worker.log
autostart=true
autorestart=true
startsecs=10

Once our configuration file is created and saved, we can inform Supervisor of our new program through the supervisorctl command. First we tell Supervisor to look for any new or changed program configurations in the /etc/supervisor/conf.d directory with:

sudo supervisorctl reread

Followed by telling it to enact any changes with:

sudo supervisorctl update

Once our programs are running, there will undoubtedly be a time when we want to stop, restart, or see their status.

sudo supervisorctl status

For restart your celery instance:

sudo supervisorctl restart your_proj_celery